Furthermore, the semiconductor body has a semiconductor zone of the first conduction type, which semiconductor zone adjoins the gate insulator and is embedded into the epitaxial layer and is also called body zone and in which semiconductor zone the MISFET channel extends beneath the gate insulator. A drift zone of the second conduction type extends between the source electrode or the body zone and the drain electrode in the epitaxial layer. The length of said drift zone is critical for the dielectric strength of the lateral MISFET. However, the on resistance of lateral MISFETs of this type is actually increased as the drift path becomes greater and the possible reverse voltage thus becomes higher.
The document DE 198 28 191 C1 discloses a lateral MISFET of this type, this MISFET, which is referred to as a lateral high-voltage transistor, having a semiconductor body whose semiconductor substrate is weakly doped with the first conduction type. In the case of the known lateral high-voltage transistor, the epitaxial layer has pillar-type trenches in the epitaxial layer that are arranged in rows and columns in the drift zone between the source electrode and the drain electrode, the trench walls being highly doped with a dopant of the first conduction type. A PN junction is thus formed with respect to the epitaxial layer having a complementary conduction type. The PN junction corresponds to the pillar structure of the trenches introduced into the drift zone.
These pillar structures are not completely depleted of free charge carriers during the taking-up of voltage in the off-state case. They can thus serially take up the potential that is attained with the expanding space charge zone between source and drain at the corresponding pillars. Consequently, the structure disclosed in the document DE 198 28 191 C1 realizes a voltage divider function which makes it possible to permit a higher doping for the drift zone and hence to reduce the on resistance of the MISFET. However, the introduction of highly doped pillar structures that are not depleted in the off-state case, particularly for high aspect ratios of the pillars, is difficult in terms of process engineering and cost-intensive under certain circumstances.